The optical design of an fundus camera contains several challenging requirements: The image needs to be sharp and evenly illuminated with a brightness high enough to overcome noise in detection. The field-of-view should be wide enough to capture a large section of the retina. The image needs to be free from glare. Particularly reflections from lenses of the fundus camera, from the cornea and from the crystalline lens of the eye easily spoil the quality of an image. It is also desirable that imaging can be performed with undilated pupils, i.e. in a non-mydriatic way. Preferably the device should allow hand-held operation. Finally, the device should be compact and easy to align with the eye during the imaging, and the working distance needs to be long enough.
There have been attempts to build a good ophthalmoscope. In the prior art, problems related to reflections have typically been addressed by using a black-dot conjugate method together with suitable shaped forms of the lenses common to illumination and imaging. However, they impair the quality of the image by increasing aberrations, or limit the usable field-of-view. Therefore, there is a clear need for a proper ophthalmoscope.